# In the upper air, do pilots use flaps to generate lift as well slow down an aircraft?

ToUsIf
• In the upper air, do pilots use flaps to generate lift as well slow down an aircraft? ToUsIf

I know, flaps are mostly used during take-off or landing to generate both lift and drag simultaneously.

I am wondering if the pilot uses flaps to generate more lift so that they can climb in less distance (due to drag of flap) and possible reasons for doing it. I have an idea that the flight control system may prohibit flap deployment above a certain altitude or at higher speeds due to flap structural limitations.

• It's a little complex, but here is a shot. Take a look at the following graph:

What you can see is multiple airspeeds. For a plane, the rate of cruise is maximised around Airspeed B is reached- this is when the difference between power available and power required is the greatest and therefore the most excess energy is available for climb.

The slope here indicates how much power is necessary for that airspeed- the steeper the curve, the worse it is. The value is really high for airspeeds all the way to left.

If you were to deploy the flaps, you would sort-of shift the power required curve to left- adding drag, reducing the difference between the power available and power required, reducing the maximum rate and in the process increasing the power necessary.

In the equation above, you want to increase lift. Yes, you can do this with flaps- it would increase CL. As you yourself state, it takes a lot of drag to use flaps and slats. Another option is to increase velocity. This is more efficient and uses less energy.

The reason we need is flaps is since as the velocity drops for landing, we need to increase the CL to maintain sufficient lift for landing. Airspeed for B for landing though is much too fast, so you want to slow down to the left side of the graph. See this post on a little more detail on this relationship.

As for flap limitations, they appear to be 20,000 ft for the Boeing 737- Mostly because boeing found them unnecessary to use at higher altitude.

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• I know, flaps are mostly used during take-off or landing to generate both lift and drag simultaneously. I am wondering if the pilot uses flaps to generate more lift so that they can climb in less distance (due to drag of flap) and possible reasons for doing it. I have an idea that the flight control system may prohibit flap deployment above a certain altitude or at higher speeds due to flap structural limitations.

• I recently read about flap load relief systems in some aircraft that attempt to prevent flap overspeeds by automatically retracting flaps under certain conditions. Are these systems common on all large aircraft or are they specific to just a few? How do they work (i.e. under what conditions will they retract flaps)? Do they prevent the possibility of overspeeding flaps altogether, or do they just make it less likely to happen?

• I know aircraft commonly have rotary actuators to extend and retract the flaps. I am not sure how many but I think I read two per flap on a 747. My question is what is the result if one actuator fails? I don't know if more then one needs to fail in order for a flap not to extend or retract. I am mostly wondering if could cause an aircraft turn-back because somebody told me it could. However that does not seem right to me. I thought the flaps are extended before take-off so that worst case scenario prior to flight is a minor flight delay to replace it. I suppose if it failed just prior

• When I extend my flaps to 10 degrees, what exactly is the 10 degrees measuring? Is this referring to the angle of the flap blades themselves, the new angle of the wing chord, the change in the new critical angle of attack or something else?

• Most wings suffer from induced drag due to a pressure difference above and below the wing causing air to sneak around the tip, forming a vortex. There are various methods to minimize these effects...? Or are they still causing induced drag, just in a way I'm not able to think of with my limited fluid dynamics experience? I've read somewhere that a traditional bi-plane design is less efficient due... of the lower wing, and both wings would of course generate normal drag by cutting through the air, but I'm only interested in the induced drag at this point.

• I know on the 737, the leading edge slats deploy at the first flap setting, and the trailing edge flaps deploy after that at higher flaps settings. Why do the slats deploy before the trailing edge flaps?

• Full flaps on takeoff flyingfisch

Are full flaps ever used on takeoff? One flying book I read strongly discouraged anything more than quarter flaps on most planes due to the amount of drag produced. I was just wondering if there are any scenarios where full flaps might be necessary.

• on to state how much flap should be used in what conditions, and then he finishes with this: Let us then raise the flaps in gusty or crosswinds as soon as the wheels touch down. To wait until it is time to taxi doesn't help slow the plane very much, and flaps do constitute a hazard in gusts. Besides, it is surprising how much a small pebble costs when it goes through a flap. Is he right... flaps down. After the wheels were on the runway he relaxed, never realizing that a plane is not landed until the switches are cut. Because he still had airspeed and because full flaps lowered

• See Wikipedia:Drag polar and Wikipedia:Polar curve (aviation) for example. These curves are not on a polar coordinate system. Why are they called polars?

• I have heard pilots talk about flaps and slats, seemingly interchangeably. Is there a difference between a flap and a slat?

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